Anyone who has turned up the music in a car knows that sound doesn’t always reach everyone the same way.
The driver might enjoy perfect clarity, while passengers in the back or on the sides hear something very different.
That’s because car cabins have complex shapes, and speakers naturally direct sound unevenly.
But scientists in China have developed a clever solution using the mathematics of nature—fractal geometry—to make car audio sound better for everyone.
The research, published in the Journal of Applied Physics, describes a new “fractal metamaterial” that can reshape sound waves to distribute them more evenly throughout a vehicle.
The team drew inspiration from the Koch snowflake, a well-known fractal pattern that looks like a six-pointed snowflake made from an endlessly repeating triangle design.
Fractals are fascinating because no matter how much you zoom in, each part looks like a smaller version of the whole.
When sound waves hit objects similar in size to their wavelength, they bend around edges in a process called diffraction.
This bending helps spread sound—but only to a limited degree. The researchers realized that the repeating edges of a fractal could boost this effect dramatically, bending sound waves more effectively without making the speaker setup bulky.
“Fractal structures, whose edges grow with each level of repetition, offer a promising way to manage diffraction and improve how sound spreads,” explained study author Ming-Hui Lu.
As the fractal’s complexity increases, its edges multiply while the overall size stays the same. That means the device can bend sound waves across a wide range of frequencies, giving a more balanced sound experience inside the car.
To test their design, the team molded a precise Koch snowflake pattern into a thin metamaterial and placed it in front of a car speaker. Measurements of sound levels at various seats showed a striking improvement—sound pressure differences between passengers dropped significantly, even at high frequencies where many speaker systems struggle.
“The fractal metasurface successfully produced a more uniform sound field, improving the listening experience for everyone in the car,” Lu said. The results held up in both laboratory and real car tests, confirming the technology’s reliability.
The researchers are now working with Chery Automobile Co. to explore how this innovation could be integrated into future vehicle designs. They also plan to refine the metamaterial to cover an even broader range of sound frequencies, potentially ushering in a new era of crystal-clear car audio.
Source: American Institute of Physics.
